This invention is in the field of structuring particles. Specifically, surfactant systems comprising a sufficient concentration of a surfactant that can structure a non-aqueous liquid.
Structured liquids, for example, gels and certain non-Newtonian fluids, have numerous applications and have gained great favor among consumers. For example, many paints are supplied as liquids that are structured in situ, that is, the structure is established in the container as the paint is mixed. Paint is typically structured in an attempt to evenly suspended fine, solid pigment particles in the liquid paint carrier. But as most consumers of paint products are well aware, more often than not when paint is purchased the pigment particles have settled to the bottom of the container. This occurs when the structure of the paint is broken down by the normal jostling during shipping and handling of the containerized paint. Once the structure is broken down it cannot be reestablished, and the paint must be shaken or stirred before each use to resuspend the pigment particles. The necessity of shaking or stirring, which is often a messy procedure, is the bane of painting.
Among the most common structurants for liquid compositions are clay compounds. While clay provides good in situ structuring for certain liquid environments, clay structured systems are inherently unstable. Liquids structured with clay and other conventional structurants rely of a delicate balancing of particle forces that when disturbed cause the structure to break down. Specifically, two particles are often attracted due to natural forces such as van der Waals forces. But if brought too close together two particles will normally repel one another due to natural repulsive forces between particles. Also, entropy works to break down weakly structured systems. Hence, structured liquids are fragile and the structure is easily broken down.
Conventional surfactants have also been used to structure liquids. But surfactant structures are inherently weak because they rely on a weak ordering of the surfactant molecules. More specifically, surfactants molecules are know to arrange themselves wherein the head groups agglomerate forming micelles or inverse micelles, which individually can act as structuring bodies. Unfortunately, as is the case with clay structured liquids, the structure relies on relatively weak intermolecular attractive forces, rather than actual chemical or physical bonding. Liquids structured with conventional surfactants are generally unstable.
Additionally, structure within a liquid can be broken down by the addition of chemicals that adversely affect interparticle forces. For example, liquids structured with clay, surfactants or polymers are sensitive to the electrolyte composition of the liquid. Unfortunately, electrolytes are desirable for use in many liquid compositions such as heavy duty liquid laundry detergents, which makes the structuring of these liquids especially difficult. Often the instability problems of structured heavy duty liquid detergent compositions are addressed by maintaining very tight controls over the formulation of these detergents, and by using less than the amount of certain chemicals than would be dictated by performance alone. In other words, performance characteristics and economics are often sacrificed to achieve the desired liquid aesthetics.
These and other problems are solved by the structuring particles of the present invention. The problems associated with structuring liquids that are discussed above, occur in non-aqueous solutions, for example, oil base paint, as well as aqueous systems. The present invention, however, is primarily directed to structuring non-aqueous liquids.
To address the problems and shortcomings of available liquid structurants there is a continuing need for new compositions that can produce relatively stable structured liquids. Moreover, there exists a need for a liquid structurant that is relatively insensitive to the chemical composition of the liquid being structured, and is tolerant of normal physical agitation.
The present invention provides a surfactant system capable of structuring a non-aqueous liquid composition, wherein the surfactant system comprises at least about 5%, by weight of a structuring particle. The surfactant system preferably further comprises a surfactant selected from the group consisting of anionic, nonionic, cationic, amphoteric surfactants and mixtures thereof.
In one preferred embodiment of the present invention, there is provided a well dispersed mixture of at least about 25%, by weight of the surfactant system and a C12-13 alcohol ethoxylate with an average degree of ethoxylation of 5, which results in the mixture having a yield of at least about 2.0 Pa when measured at 20 secxe2x88x921 and 25xc2x0 C.
In another preferred embodiment of this invention, the surfactant system and the structuring particles exhibit a peak when measured by SAXS x-ray diffraction, and the peak""s center is between about the 1.5 to 2.5 positions on the 2 theta axis.
The structuring particles are preferably not soluble in non-aqueous liquids such as butoxy propoxy propanol, cyclohexane, nonionic surfactants and mixtures thereof. Also, the structuring particles are preferably soluble in aqueous liquids.
In one preferred embodiment of the present invention the structuring particle is a particle comprising sulfate and a surfactant which comprises a sulfonate head group, and more preferably the structuring particle comprises sulfate and C6-20 linear alkyl benzene sulfonate.
In another aspect of the present invention a method of making a structuring particle is provided. The method comprises the steps of:
a) making a surfactant paste comprising an alkali metal surfactant, preferably sodium linear alkyl benzene sulfonate, and an aqueous solution, which is preferably water, in a ratio of from about 2:1 to about 1:4, preferably from about 1:1 to about 1:3;
b) combining the paste and an alkali metal sulfate, preferably sodium sulfate, in a ratio of metal surfactant to metal sulfate of from about 4:1 to about 1:2, preferably from about 3:1 to about 1:1;
c) agitating the paste and the metal sulfate until a well dispersed mixture is obtained;
d) allowing the well dispersed mixture to stand with no agitation for at least about two hours, preferably at least about 6 hours and most preferably at least about 12 hours; and
e) drying the well dispersed mixture, preferably on a drum dryer.
Surprisingly, it has been determined that the surfactant systems and structuring particles of this invention can structure non-aqueous solutions in the presence of numerous chemical compositions that can break-down conventional liquid structures. The ability to structure a variety of different non-aqueous solutions allows the surfactant system and structuring particles of this invention to be useful in numerous commercial liquid compositions, for example, to suspend particles in a liquid environment. Paint products, agricultural products and liquid laundry compositions are but a few of the commercial applications for the structurants of the present invention. In the paint arena, an ancillary benefit is achieved by using the surfactant systems and structuring particles of this invention. Because the structurant may also be a surfactant, paint is more easily removed from the brushes and rollers due the natural surfactancy of the paint/surfactant combination.
In addition to their ability to structure non-aqueous liquids, the surfactant systems and structuring particles of this invention have shown superior, and unexpected dissolution properties in aqueous solutions. For example, conventional linear alkyl benzene sulphonate dissolves in water at an appreciably slower rate and to a lesser degree than does a surfactant system comprising conventional linear alkyl benzene sulphonate and at least about 5% of structuring particles of sulfate and linear alkyl benzene sulphonate, that is, at least about 5% of a structuring particle, according to the present invention.